1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an in-plane switching (IPS) mode liquid crystal display device and a method of fabricating the same.
2. Discussion of the Related Art
Flat panel display (FPD) devices having portability and low power consumption have been subject of recent research and development since the coming of the information age. Specifically, a liquid crystal display (LCD) device, a plasma display panel (PDP) device, an electroluminescent display (ELD) device and a vacuum fluorescent display (VFD) device have been developed as FPD devices. Among the various types of FPD devices, liquid crystal display (LCD) devices are widely used as monitors for notebook computers and desktop computers because of their high resolution, color quality and superior image movement.
In general, an LCD device includes a first substrate, a second substrate, and a liquid crystal layer between the first and second substrates. In an LCD device, an alignment direction of liquid crystal molecules in the liquid crystal layer is controlled by a vertical electric field generated between a pixel electrode on the first substrate and a common electrode on the second substrate, thereby displaying images. In an LCD device using a vertical electric field, however, a response speed of liquid crystal molecules and a viewing angle of the LCD device are relatively low.
To solve the above problems, an in-plane switching (IPS) mode LCD device has been suggested. In an IPS mode LCD device, a pixel electrode and a common electrode are formed on a single substrate and an alignment direction of liquid crystal molecules is controlled by a horizontal electric field generated between the pixel electrode and the common electrode. Accordingly, a response speed of the liquid crystal molecules and a viewing angle of the LCD device are improved.
FIG. 1 is a schematic plane view showing an array substrate of an IPS mode LCD device according to the related art. In FIG. 1, a gate line 111, a data line 141, a thin film transistor (TFT) “T,” a common line 115, a pixel electrode 161, and a common electrode 117 are formed on a substrate. The gate line 111 crosses the data line 141 to define a pixel region “P” and the TFT “T” is connected to the gate line 111 and the data line 141. The TFT “T” includes a gate electrode 113 connected to the gate line 111, a semiconductor layer 131, a source electrode 143 connected to the data line 141, and a drain electrode 145 separated from the source electrode 143. The pixel electrode 161 is connected to the drain electrode 145.
The pixel electrode 161 and the common electrode 117 are parallel to and spaced apart from each other. When voltages are applied to the pixel electrode 161 and the common electrode 117, a horizontal electric field is generated between the pixel electrode 161 and the common electrode 117. Accordingly, a domain area “D” of liquid crystal molecules is defined by the pixel electrode 161. The liquid crystal molecules in the domain area “D” are re-aligned by the horizontal electric field generated between the pixel electrode 161 and the common electrode 117 when voltages are applied.
The pixel electrode 161 and the common electrode 117 are both formed to be parallel to the data line 141. Thus, the liquid crystal molecules in the domain areas “D” of the pixel region “P” are re-aligned along an equal alignment direction, and the domain areas “D” of the pixel region “P” have equal optical properties. As a result, the optical properties in the domain areas “D” are not compensated, and the LCD device has different contrast ratios at top, bottom, left, and right portions thereof. The difference in contrast ratios causes a reduction in viewing angle and a deviation of color coordinate at the top, bottom, left, and right portions. For example, deterioration—such as a yellow shift phenomenon and a blue shift phenomenon may be observed in an IPS mode LCD device according to the related art. Moreover, an additional common line 115 that does not function as a common electrode for generating a horizontal electric field is formed in the pixel region “P” reduces the aperture ratio of the IPS mode LCD device.